Prepare the Meat Sauce: In a large pot, heat olive oil over medium heat and add chopped onions with a pinch of salt until translucent. Incorporate ground beef until no longer pink, then stir in tomato sauce and cinnamon. Bring to a simmer and season with salt, letting it stew with a lid on for three hours.

Cook the Noodles: Bring salted water to a boil and cook pastitsio noodles until al dente—about one or two minutes less than package instructions. Drain thoroughly and allow to cool slightly.

Mix Eggs with Noodles: In a large bowl, combine cooled noodles with one beaten egg, ensuring they are evenly coated to help bind them together.

Layer Ingredients in Pan: Preheat oven to 350ºF. Drizzle olive oil in the lasagna pan, spread egg-coated noodles evenly, add a layer of cheese, and top with most of the meat mixture, leaving space for béchamel.

Prepare Béchamel Sauce: In a heavy-bottomed pot, melt one stick of butter over medium heat, whisk in flour, and cook for under two minutes. Gradually add five cups of milk while whisking until just boiling, then remove from heat.

Combine Béchamel Mixture with Eggs: In another bowl, beat three eggs with half a cup of milk, then slowly incorporate this mixture into the béchamel pot while whisking consistently.